My best guess is the diagnosis is wrong. Converters do not overheat on their own. They overheat in response to some other problem. That problem can also cause running problems as you described. If the engine runs fine at any time, the converter is not plugged.
The Engine Computer requests a little too much fuel to go into the engine, then it switches to too little fuel. It switches back and forth a couple of times per second. When the fuel is reduced, (lean), the unburned oxygen is momentarily stored in the catalyst material. A fraction of a second later, when that extra unburned fuel shows up, it mixes with the stored oxygen and is burned, then goes harmlessly out the tail pipe. There is supposed to be fuel being burned in the converter but it's that excessive fuel that is the problem.
When the problem occurs, check for a lot of black smoke coming from the tail pipe. That is a sure sign of way too much fuel going into the engine. Next, listen to the sound of the exhaust. It should make the normal "putt-putt" sound. If the converter is plugged, it will sound more a steady, quiet hiss.
Saturday, January 14th, 2012 AT 6:54 AM